1. Field of the Invention
The present invention relates to data transfer apparatus utilizing infrared rays, and more particularly to a data transfer apparatus for sending a large quantity of data by utilizing a base band mode of infrared rays based on amplitude shift keying (ASK).
2. Description of the Related Art
In recent years, communication apparatus such as cordless telephones, mobile communication terminals and wireless remote control devices have become prevalent in our daily life. In addition, the realization of wireless LAN has been promoted, and wireless communication is getting more and more important than ever before.
As one mode of relatively short distance wireless communication, attention has been directed to a data transmission mode utilizing an ASK-based base band mode of infrared rays.
Normally, this particular data transmission mode sends data in bytes by using an asynchronous method.
As shown in FIG. 10, one transmission unit of transmission data to be sent is represented by a start bit "1," 8-bit long transmission data (B0 to B7), a parity bit and a stop bit "0". In other words, the transmission data is represented by 11 bits in total.
Data transmission using infrared rays means data transmission by the blinking of LED's that emit infrared rays.
Specifically, infrared rays emitting LED's are blinked with a signal that has been modulated with a sub-carrier wave frequency for a predetermined time when the data bit assumes "1". When the signal is to be modulated with 500 KHz sub-carrier wave, LED's repeat 0.5 million blinkings for continuous transmission of "1" for one second. When the data bit assumes "0", LED's are quenched for a predetermined time.
On the receiving side of the data transmission, infrared rays are received with a receptor such as photo-diodes, photo-transistors or the like. Then transmission data is demodulated by letting the data to pass through amplifiers, filters and demodulation circuits.
In addition, to secure the transmission quality of communication and to continuously send a large quality of data on the order of several tens of Kbyte, data is actually sent in accordance with communication circuit control procedures such as the basic procedures or HDLC procedures for performing error detection and retransmission.
As described above, in a data transmission mode in which infrared rays emitting LED's is blinked for sending data "1", the LED blinking time is extremely prolonged as shown in FIG. 11 when FFH data is sent. In such case, heat radiation of LED's becomes very large and the deterioration in the performance of data transmission is quickened.
The deterioration in the performance in data transmission owing to heat radiated from LED's will lead to the shortage in luminescent power from LED's and delay in the luminescence. This will affect the time properties of LED blinking. In the end, the quality of communication is deteriorated such that light cannot be received at the receiving side of data transmission.
Therefore, the following methods have been considered to inhibit heat radiation of LED's.
1) To minimize the continuous transfer of "1", time is set for suspending data transmission for a predetermined time, for example 10 msec immediately after data has been sent for a predetermined time, for example, 1000 msec.
2) A predetermined time is set for suspending data transmission immediately after one transmission unit of transmission data has been sent. For example, as shown in FIG. 12, 5-bit compulsory suspension time is set immediately after the stop bit has been sent.
3) As shown in FIG. 13, data is sent with RZ (return to zero) mode having both blinking and quenching period of LED per one bit.
In all the three methods described above, time is taken for suspending data transmission for quenching LED's in a concentrating or scattering manner to cool LED's.
All the above methods have a drawback of slowing the communication speed without exception though such methods serve to moderate heat radiation of LED's and prolonging the life of LED's by setting a time for cooling LED's. In addition, the RZ mode has a smaller blinkings of LED's per one bit. The reliability of data transmission is a problem in communication in an environment in which various troubles are likely to be generated in data transmission through space.
Although data transfer speed per byte is made faster than wire transmission speed by utilizing infrared rays, there is a fear that an originally intended high speed communication cannot be performed by setting suspension time for inhibiting heat radiation from LED's.
In addition, deterioration in the communication reliability results in a frequent retransmission of data by means of communication control procedures, which slows down the communication speed.
As light emitting devices used for preventing the deterioration in the performance owing to heat, the following related inventions are available.
Japanese Published Unexamined Patent Application No. HEI 4-243183 laid open on Aug. 31, 1992 describes a semiconductor laser apparatus providing a construction comprising a photoconductive channel layer and a clad layer both formed of a mixed crystal having a difference dimension, the photo-conductive channel layer having a distribution feedback portion formed thereon whereby a single mode of laser light can be stable oscillated.
Furthermore, Japanese Published Unexamined Patent Application No. HEI 5-13843 laid open on Jan. 22, 1993 describes a heat radiation component comprising a stem having a portion on which a semiconductor element is mounted, a gas phase synthesis polycrystalline diamond layer covering the surface of the portion of the stem where the semiconductor is mounted, whereby heat conduction efficiency from the semiconductor laser element is improved and the deterioration of properties owing to heat generation at the semiconductor laser element can be prevented.
Furthermore, Japanese Published Unexamined Patent Application No. HEI 5-211283 laid open on Aug. 20, 1993 describes an optoelectronics package for optical communication between a light transmitter and a light receiver arranged on different substrates without using an optical fiber or a photoconductive channel.